Hydroprocessing of coal



United States Patent 3,502,564 HYDROPROCESSING 0F COAL Russell L.Hodgson, Walnut Creek, Calif., assignor to Shell Oil Company, New York,N.Y., a corporation of Delaware No Drawing. Filed Nov. 28, 1967, Ser.No. 686,345 Int. Cl. Cl0g [/06 US. Cl. 208--9 6 Claims ABSTRACT OF THEDISCLOSURE The in situ preparation of a hydrogenation-liqueficationcatalyst impregnated on the coal results in significant improvement incatalytic activity. Metal naphthenates and sulfides are particularlyappropriate catalysts for in situ preparation.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a process for the hydrogenation-liquefication of coal toliquid hydrocarbon oils. More particularly it relates to an improvedprocess wherein a hydrogenation catalyst is prepared on the coal itself,i.e. in situ.

Description of the prior art A practical process for converting coal toliquid fuels as a means of utilizing the extensive energy reserves inthe worlds coal deposits has been a much sought after goal since it wasfirst demonstrated nearly 60 years ago that coal could be hydrogenatedto liquid products. Particularly large research efforts were carried outin Germany prior to and during World War H and in the United States bythe Bureau of Mines following the war. The number of publications andpatents in this area is astronomical, as witnessed by a Bureau of Minesbibliography compiled at the outset of their efforts in the late 1940scontaining over 6,000 entries. [1. L. Wiley and H. C. Anderson, BureauMines Bull. 485: Part I (1950); Part II (1951); Part III (1952)]. Workon coal hydrogenation has not waned in recent years; in fact, it isapproaching fruition in the form of economical processes for convertingcoal into refinable liquid products.

Several unique problems associated with the conversion of coal torefinable liquid products result from its chemical and physical nature.Not only is the starting raw material a solid, but even if completeconversion of the organic matter were possible, an appreciable amount ofinorganic ash remains. The amounts of nitrogen, sulfur, and especiallyoxygen which must be removed are far in excess of those normallyencountered in processing even the most refractory heavy petroleum oils.Finally, the condensed nature of the coal molecule results in a lowhydrogen/carbon ratio, necessitating the addition of large amounts ofhydrogen.

In general, processes developed for conversion of coals into liquidproducts require that the coal is first broken down to a liquid statewhich can be processed further by more or less conventional petroleumrefining techniques such as hydrocracking, reforming, etc. While thefirst step may be merely a thermal treatment, there are significantadvantages for catalytic hydrogenative decomposition or liquefication.However, the most effective means known require very high pressures inthe range of 2000 to 6000 psi. and temperatures in the range of 500 C.Thus, the conversion of coal is generally conducted in a multistageprocess in which the first stage often involveshydrogenation-liquefication followed by extraction of the resultingmiddle oils. A similar process is Gorin, US. 3,143,489

ice" Numerous catalysts for the hydrogenation reactionv have beenproposed. These are added to the coal in various ways. One method is tohydrogenate coal extract in an ebulating bed of the catalyst. Anothermethod is to tumble powdered coal with the catalyst. impregnation ofcoal with a catalyst has also been proposed and is an effective method.In impregnation, the coal is slurried with a catalyst which is dissolvedor dispersed in aliquid medium and the liquid removed by evaporation,etc. Thus efficient dispersion of the catalysts, necessarily used insmall amounts, with the coal is effected. Despite the multitude ofsuggestions there is still great incentiveto improve activity for thehydrogenation so as to obtain conversion at lower temperatures andpressures.

Catalysts which have been found effective are metal compounds,particularly metal halides and metal sulfides.

. Another class of catalysts are metal naphthenates, some of which arehighly active. Naphthenates also have the advantage of being hydrocarbonsoluble, allowing the use of a hydrocarbon impregnation medium and thusbetter contact and dispersion.

SUMMARY OF THE INVENTION It has now been discovered that preparation ofthe catalytic compounds, in situ, results in far more effectivecatalytic action than mere impregnation with the final {catalyticcompound. By in situ preparation it is meant the formation, from ionicspecies and components of the desired catalytic chemical compound inadmixture with the coal, i.e. after impregnation of the coal with onecomponent.

In broad aspect, the invention is a process for the hydrogenation ofcoal wherein a hydrogenation catalyst is formed on coal in situ byimpregnation of the coal with a component of the desired catalyticcompound followed by subsequent conversion to a desired catalytic formof the metal. For example powdered coal is impregnated with a metal saltwhich is converted to the metal sulfide.

In a preferred embodiment of the invention, the process is effected witha catalyst selected from metal sulfides and metal naphthenates which areprepared in situ on the coal.

Surprisingly, it has been discovered that the effectiveness of a metalsulfide or naphthenate catalyst is greatly increased if the coal isfirst impregnated with a metal salt which is subsequently converted, inits dispersed state, to the corresponding sulfide or naphthenate.Particularly impressive are some of the in situ prepared sulfided metalnaphthenate catalysts. The effectiveness significantly surpasses that ofa single step impregnation of the catalytic compound itself.

In an embodiment of the invention powdered coal is impregnated with asiutable solution of a metallic salt of the hydrogenative metal, e.g.molybdenum chloride, the solvent removed and the salt then sulfided byan appropriate sulfur compound which either reacts with, or decomposesto a form which can react with the metal salt dispersed on the catalyst.Hydrogen sulfide is a convenient and especially suitable sulfidingmedium. This embodiment has the additional advantage of allowingimpregnation of catalytic compound such as metal sulfides which becauseof their insolubility cannot be impregnated directly on the catalyst.Heretofore insoluble compounds could only be incorporated by suspension.

Hydrogenation after impregnation may be accomplished by various meansknown in the art. In a continuous hydrogenation process, the powderedcatalystimpregnated coal is generally formed into a paste with a heavyhydrocarbon oil, e.g. a cycle oil and passed into a hydrogenation zone.Any other method of continuous or batch hydrogenation may be used forthe coal impregnated according to the inventioneither batch orcontinuous with or without a solvent. The hydrogenation may be carriedout over a wide range of conditions depending upon the catalyst used,the type of coal being processed and desired degree of conversion. Withcoal impregnated with catalysts prepared in situ by the method of theinvention; in general, lower temperatures and hydrogen pressures arerequired.

Temperatures in the range of ZOO-600 C. and hydrogen pressures from500-3000 p.s.i.g. may be used. With conventional impregnations, i.e. thecoal being impregnated with the catalytic compound itself, temperaturesin excess of 500 C. are usually employed to eflFect substantial coalconversion at hydrogen pressure in the range of 2500 to 3000 p.s.i.g.With coal impregnated with catalysts formed in situ, hydrogenation cangenerally be effected at lower temperatures, in the range of 350-450" C.and at hydrogen pressures in the range of 1000-2000 p.s.i.g.

It has also been found that successive hydrogenations are advantageousto increase conversion, preferably without intermediate impregnation ofadditional catalyst. With coal impregnated with catalyst prepared insitu, a series of hydrogenations of successive extractive residues leadsto a significant increase in conversion.

Any hydrogenation metal salt which can be converted to metal sulfidesand/ or naphthenates are suitable for the practice of the invention.Nickel, tin, molybdenum, cobalt, iron and vanadium salts are especiallypreferred, particularly the halogen salts of these metals.

The process of the invention may be effectively carried out for thehydrogenation of any type of coal as for example, bituminous,subbituminous or lignite coal. The coal is preferably ground orpulverized into a powder to increase the efiiciency of impregnation.

Any suitable solvent may be used as a carrier for the impregnate, waterbeing of course a logical choice in many instances. However, a lowerboiling solvent which can be easily recovered is desirable in manyapplications. The requirements are solubility of the impregnate in thesolvent and non reactivity of the solvent with the coal. For example,ether has proved a particularly suitable solvent for impregnation ofsuch salts as molybdenum chloride. The concentration of the impregnatein the solvent is not critical. It should be as high as possible on theone hand to minimize solvent requirements and recovery and on the otherhand not too high to impair the dispersion or to render the physicalproperties of the solution unmanageable. Use of appropriateconcentrations within these broad limits is within the skill of those inthe art.

When the catalyst is converted, in situ, to the sulfide, any sulfurcompound which gives the sulfide compound, i.e. which reacts with theimpregnated metal salt is suitable. Hydrogen sulfide is preferred. Againconcentration is not critical and any available hydrogen sulfidecontaining gas may be used, as, for example, hydrogen sulfide oif-gasfrom refinery streams are appropriate. Relatively pure hydrogen sulfidemay, of course, be used. Elevated temperatures are desirable forsulfiding, for example, temperatures in the range of 200-500" C. aresuitable. In general, sufficient sulfur should be added to convertsubstantially all the metal to the sulfide form.

Sulfiding may be conducted in the same reactor vessel as thehydrogenation reaction or in a separate sulfiding reactor. In one aspectof the invention the catalyst can be impregnated with a metal salt, asfor example, molybdenum chlorides, the solvent removed and theimpregnated coal passed to a suitable reactor capable of high pressureoperation where it is sulfided and subsequently hydrogenated. Sulfidingand hydrogenation can be carried out in separate zones of the samecontinuous reactor, sulfiding preceding hydrogenation.

Metal naphthenates are known to be very effective hydrogenationcatalysts. These are conventionally incorporated with the coal, byimpregnation of the preformed metal naphthenate, e.g. cobaltnaphthenate. In the process according to the invention significantcatalytic enhancement results if the metal naphthenate is formed on thecoal by impregnation of the coal either with the metal ion or thenaphthenate ion followed by conversion of the impregnated species to themetal naphthenate. For example cobalt naphthenate can be prepared byimpregnation of powdered coal with naphthenic acid and then contactedwith a cobalt halide salt to form cobalt naphthenate. It is especiallypreferred to further react the metal naphthenate with a sulfur compoundsuch as H S. The exact nature of the resulting catalytic compound is notknown but the results are striking as will be illustrated in theexamples.

The following examples serve to illustrate but are not to be consideredlimiting the invention.

EXAMPLE I A series of experiments were made on thehydrogenation-liquification of Illinois No. 6 coal. Representativeanalysis of this coal is shown in Table I.

Table I Elemental analysis (percent w.): 1 Illinois No. 6 coal Carbon78.9 Hydrogen 5.4 Nitrogen l.5 Sulfur 4.3 Oxygen 9.9 H/C (atomic ratio)0.8 Moisture (percent w.) l0.9 Ash (percent w.) 13.3

1 Analysis on a moistnre-and-ush-free (MAF) basis.

To illustrate the effectiveness of the in situ preparation of metalsulfide catalysts according to the process of the invention, samples ofpowdered coal were impregnated with MoCl which was converted to thesulfide form. The powdered coal was impregnated from an ether solutionof the MoCl the ether being subsequently removed by evaporation.

One sample was simply mixed with MoS for comparison. MoS could not beimpregnated in the conventional means because of its insolubility. Thecoal with incorporated catalyst was placed in an autoclave reactor at400 C. for one hour under hydrogen pressure maintained at 1400-1500p.s.i.g.

After hydrogenation the products were first collected by venting thereactor at 200 C. to obtain gases, liquids boiling up to 200 C., andwater. Next the residue was extracted for /2 hour with each of threeportions of refiuxing benzene and water followed by a 24 hour Soxhletextraction with methyl ethyl ketone. The extent of reaction wasdetermined both from the recovered products and from the loss in weightof the coal and is reported on a moisture-and-ash-free (MAF) basis interms of solubilization and conversion, defined as follows:

Extractable products Conversion (percent w. MAF) Coal fed Recoveredresidue Coal fed The results are shown in Table II.

TABLE II Solubilization, Conversion, percent w. percent w. Run N 0.Catalyst MAF MAF 3-1 1 2% MOS 32 34 59 -64 79 as 1% M0015 60 b5 A-5 1%M0015 sulfided 76 82 A-6 0.1% M0015 30 47 A-7 0.1% M0015 sulfided 52 L541 MoS mixed with powdered coal. 2 MoCl was impregnated from an othersolution.

These results clearly show the eifett of in situ preparation of sulfidecatalysts. In every case the solubilization and conversion was markedlyincreased by in situ sulfiding.

It should be noted that the conditions are very mild by conventionalstandards. While a number of catalysts give greater solubilizationconversion at 500 C. and 3000 psi. H pressure than the present results,the severe conditions are serious detriments to the commercialfeasibility of the process and the increased conversion at the mildconditions used is a significant achievement.

It is also demonstrated in this example that catalyst in very lowconcentration, e.g. 0.1% w. are eifective when incorporated into thecoal in situ.

EXAMPLE II Additional experiments were made by impregnating powderedIllinois No. 6 coal with various salts which were converted to thesulfide in the same way as described in Example I. Conditions forhydrogenation were also the same as described in Example I.

The results are shown in Table III.

The enhancement in catalytic effectiveness is clearly evident resultingin the case of sulfided (NH Mo O in nearly triple the solubilization andconversion over thermal hydrogenation without catalyst but otherwiseunder the same conditions.

EXAMPLE III "Elfective impregnated catalysts are the metal naphthenates.These are of commercial interest because of the availability ofnaphthenic acids in crude oil. These acids are currently removed fromthe oil and frequently disposed of as fuel. Several experiments withboth nickel and cobalt naphthenates were carried out with results beingshown in Table IV. The conditions were the same as in Example I.Impregnation with naphthenic acid itself gave only a slight increase inreaction over thermal treatment without catalyst. The in situpreparation of nickel naphthenate at a controlled pH was more eifectivewith both the solubilization and conversion approaching 40%. Cobaltnaphthenate, previously prepared, as a 6% metal-containing mixture wasimpregnatedto the extent of 2% w. (0.1% w. Co) to give solubilizationand conversion of 35-40%. Sulfiding of this previously preparedn-aphthenate material after impregnation did not affect the results. Thepreparation of cobalt naphthenate in situ from naphthenic acid andcobalt sulfate gave improved results, the solubilization and conversionbeing about 45%. When this naphthenate 6 was sulfided, the coalsolubilization and conversion increased to again illustrating theadvantage of sulfiding even the naphthenate catalyst prepared in situ.

I claim as my invention:

1. A process for hydrogenation of coal comprising sequentiallyimpregnating coal with a solution containing ions of a metal, thesulfide or naphthenate of which have activity as a hydrogenationcatalyst, and with a compound that reacts with the ions to form themetal sulfide or naphthenate in situ, contacting the resultant mixturewith hydrogen at elevated temperature and pressure and recovering aliquid product therefrom.

2. The process of claim 1 wherein said compound that reacts with theions is hydrogen sulfide.

3. The process of claim -1 wherein said compound that reacts with theions is hydrogen naphenate.

4. The process of claim 1 wherein the metal is cobalt.

5. The process of claim 1 wherein the metal naphthenate is sulfidedafter sequential in situ impregnation by contacting with a sulfurcompound at elevated temperature.

6. The process of claim 4 wherein the cobalt naphthenate is sulfidedafter sequential in situ impregnation with a sulfur compound at elevatedtemperature.

References Cited UNITED STATES PATENTS 1,894,926 1/1933 Varga 208101,923,576 8/1933 Krauch et al 20810 1,946,341 2/1934 Von Szeszich 2Q;8101,950,333 3/1934 Von Szeszich 20810 2,025,882 12/1935 Michot-Dupont20'8-9 2,058,789 10/ 1936 Herold et al. 208--10 1,723,431 8/ 1929Melamid 20'8---9 2,170,976 8/ 1939 Pier 208-9 2,221,952 11/1940 Pier2089 3,143,489 8/1964 Gorin 208-8 DELBERT E. GANTZ, Primary ExaminerVERONICA OKEEFE, Assistant Examiner U.S. Cl. X.R. 20810

